As the “replacement of copper cables with optical fiber cables” gradually becomes a mainstream access mode in network technologies, the application of optical access technologies flourishes. A passive optical network (Passive Optical Network, PON) technology is an optical access technology based on point to multipoint (Point to MultiPoint, P2MP). A passive optical network system mainly includes an optical line terminal (Optical Line Terminal, OLT) located at a central office, multiple optical network units (Optical Network Unit, ONU) on a user side, and an optical distribution network for distributing or multiplexing data signals between the optical line terminal and an optical network unit. A direction from the optical line terminal to the optical network unit is defined as a downlink direction, while a direction from the optical network unit to the optical line terminal is defined as an uplink direction. The optical line terminal sends a downlink optical signal to the optical network unit and receives an uplink optical signal from the optical network unit through the optical distribution network.
In an actual application environment, to reduce maintenance costs, a receiving part and a sending part for photoelectric conversion inside the optical line terminal are normally grouped as a pluggable module and a receiving part and a sending part for photoelectric conversion inside the optical network unit are normally grouped as a pluggable module in the industry, namely, an optical module. An optical module of the optical line terminal may also have partial monitoring functions, such as an optical power detecting function, so that the optical line terminal may perform fault monitoring and fault location. Specifically, when an transmit optical power of an optical network unit is P1 (the transmit optical power value P1 may be reported by the optical network unit to the optical line terminal), the optical module of the optical line terminal may obtain, by using the monitoring function thereof, an optical power P2 of an uplink optical signal received thereby from the optical network unit and transmitted through the optical distribution network. That is, a receive optical power corresponding to the optical network unit is P2. Then, the optical line terminal may calculate an insertion loss A=P1−P2 of the optical network unit. Further, the optical line terminal may compare the calculated insertion loss value A with a theoretically standard value of a system insertion loss, to determine whether a fault occurs on the optical distribution network.
However, because optical power measurement accuracy of an optical module is limited in the prior art, there may be a certain difference between the receive optical power value P2 of the optical network unit obtained by optical power detection and an actual receive optical power value, which may result in a big difference between the insertion loss value A calculated and obtained by the optical line terminal and an actual system insertion loss value, thereby causing the optical line terminal to make an incorrect judgment on a fault condition of the optical distribution network.